It is well known that many chemical reactions are exothermic, i.e. they produce heat, and examples of such reactions include acid-base reactions.
U.S. Pat. No. 4,325,355 describes a heating system in which an exothermic reaction between a solid metal and a solution takes place in a reactor containing a heat exchanger. In the specific reaction system described, aluminium pieces are lowered into a solution of sodium hydroxide solution. During the reaction between aluminium and sodium hydroxide solution, the aluminium is converted to aluminium hydroxide with the evolution of hydrogen gas. The aluminium hydroxide reacts with the sodium hydroxide to form sodium aluminate.
DE 3539710 describes a small scale heating system comprising an outer pouch containing an inner pouch partitioned to form two chambers containing reactive chemicals. Pressurizing the pouch (for example by kneading) causes the partition wall to rupture allowing the two reactive chemicals to react to produce heat. The reactive chemicals can be sodium hydroxide and acetic anhydride. The heating system of DE 3539710 is described as being particularly useful for warming hands and feet.
GB 2381187 discloses a method and apparatus for cleaning a surface. As part of the cleaning process, a cleaning solution is heated by the mixing of chemicals in an exothermic reaction.
WO 86/01880 describes a heating system that can be used for domestic water heating and which involves a multistage process comprising a first heat exchange step in which heat extracted from sea water is used to vaporize a liquefied gas such as ammonia. The ammonia vapour then passes to a second stage where it reacts either with sodium carbonate solution or carbon dioxide in an exothermic process, the heat from which is extracted to heat domestic water.
U.S. Pat. No. 4,044,821 describes an energy conversion and storage system in which chemical compounds such as ammonia or metal hydrides are decomposed using energy from, for example, a solar energy device. The decomposition products can be recombined in a later step to produce chemical energy.
WO 2004/040645 discloses a microfluidic heat exchanger for providing small scale heating and cooling control using exothermic and endothermic chemical reactions. The addition of sulphuric acid to water is disclosed as an example of an exothermic heating source.
U.S. Pat. No. 3,563,226 describes a heating system intended for use underwater or in oxygen-free environments in which an oxidizer such as pure oxygen is reacted with a pyrophoric material such as phosphorus.
U.S. Pat. No. 7,381,376 discloses steam/vapour generators in which the source of the heat is an exothermic chemical reaction.
DE 3819202 describes a system of heat storage using molten salts.
U.S. Pat. No. 4,303,541 describes latent heat storage devices that make use of saturated solutions of salts. The salts are formed by the reaction of an acid and a base, and there is a passing reference to the possibility that the heat generated in the reaction may be used elsewhere.
My earlier patent application WO2008/102164 discloses a method and apparatus for producing a supply of a heated fluid (e.g. water) wherein the method comprises passing the fluid through a heat exchanger unit where it is heated by a heat source which derives its heat from the exothermic reaction of two or more chemical reactants.
The present invention provides an improved apparatus for making use of the heat generated by exothermal chemical reactions to heat liquids such as the water in a water supply.